1. Field of the Invention
This invention relates to an image pickup apparatus, such as an electronic imaging apparatus, mounted to and used in a microscope in order to photograph a specimen, for instance, and in particular, to an image pickup apparatus in which different optical filters can be selected and used in accordance with applications.
2. Description of Related Art
Conventional image pickup apparatuses of this type are set forth, for example, in Japanese Patent Kokai Nos. 2001-125152, 2001-296583, 2003-298855, and 2004-312552. Each of these image pickup apparatuses is designed so that an optical filter to be used can be arbitrarily selected according to the purpose of image pickup.
In recent years, as image pickup apparatuses for microscopes, imaging apparatuses using electronic image sensors such as CCDs have been popularized, and in the electronic image sensors, tendencies to a low cost and a high sensitivity as well are growing. In microscope observations, specimens with wide transmittances and reflectances ranging from high to low are handled. Consequently, there is the problem that in the imaging apparatus using an electronic image sensor with a high sensitivity, feeble flare is also imaged with a good sensitivity, and particularly, when a living specimen of high transmittance and a metallic specimen of high reflectance are photographed, flare is liable to become prominent.
When the case where a plane-parallel optical member (such as a low-pass filter or an IR cutoff filter) generally incorporated in the image pickup apparatus is mounted in an imaging optical path is compared with the case where it is demounted therefrom, an optical path length corresponding to its thickness is changed and as a result, the image-forming position of an observation image is delicately shifted. In particular, in the microscope observation that is small in focal depth as in a total reflection fluorescence observation of a living body, the shift of the image-forming position (the focal position) of the observation image produces a considerable adverse effect on the focusing condition of an image obtained through the image sensor.